METALLURGY OF CAST IRON.
that the combined carbon is toward i per cent., while in the chill the figures are reversed, the variations being not far from one-half of i per cent. The figures giving the analysis of the gray iron are given for a comparison and as a matter of information.''
"The main point in these analyses to which attention is called is the close agreement in the composition of the chills of these different wheels. If we take the ' averages of those that did and those that did not stand the thermal test, we find as follows:"
Total Carbon. Graphi'tc Carbon. Com. Carbon.
Average of wheels which stood the thermal test Average of wheels which did not stand thermal test .. .. ................................. 3-73 0.42 0.42 3-39 3.31
"It will be noted that the graphitic carbon is the same in both cases, and that the combined carbon only differs 0.08 per cent. Furthermore, the general agreement of the combined carbon of the chills in wheels from different makers is very noticeable and very remarkable. It is difficult to see how any other conclusion can be drawn from these figures than that there is no evidence, as far as the chemical composition is concerned, to show that the chills of wheels which stand the thermal test differ in their physical properties — so far at least as the physical properties depend on the chemistry of the metal — from the chill of wheels which do not stand the thermal test. Also, it seems fair to conclude that wheels made in different parts of the country and by different manufacturers do not differ very widely so far as chemical composi- 0.38 0-53 O.IO